The invention relates to a method of manufacturing a semiconductor device having at least one insulated gate field effect transistor, in which a silicon body is provided with a silicon dioxide gate insulation layer and in which a boron-doped polysilicon electrode layer is formed on said layer.
By means of a method of the kind mentioned a p-channel field effect transistor of the enhancement type can be manufactured. During said manufacture it has been found that, when a thermal treatment is carried out in an atmosphere containing hydrogen after the said process steps, the threshold voltage decreases or a field effect transistor of the depletion type instead of the desired enhancement type can be obtained.
These experiences have led to the recognition that, when field effect transistors are to be manufactured having boron-doped polysilicon electrode layers, the atmosphere may not contain hydrogen (see, for example, "J. Electrochem. Soc. S.S.S. and T.", vol. 120, pp. 146-148 (1973)).
In addition, however, there has been a growing need for methods in which the threshold voltage of a field effect transistor can be adjusted accurately, which adjustment can be achieved only in a complicated manner in the methods known so far.